What are the different ways used to ortographically show the length of vowels?

There is no end of ways to mark vocalic length across the orthographies of languages. It's either by diacritics, additional letters, special letters or some indirect marking.

Wikipedia helpfully lists the different diactritical maarks the most common of which are the macron (e.g. ā) and the acute accent (e.g. á). as well as additional letters the most common of which is vowel doubling.

To this you need to add the colon-like symbol (ː) used by IPA for vowel length. In English phonics training, the macron is used to indicate 'long vowels' but these are not contrasted by length alone but rather by quality and length (often the long counterpart being a diphthong) as in 'mat' vs. 'mate'. Even in a case where long counter part is available as in 'pit' vs. 'pete', the contrast is given as 'spit'/'spite' and 'pet'/'pete'.

Historically, you could also use separate letters such as the Greek omega vs. omicron but the length distinction has been lost in modern Greek.

As whole, the question of contrastive and non-contrastive vowel length is much more involved however. Things like stress, diphothongization and allophonic variation get involved so it's rarely as simple as establishing a long/short contrast across the whole vowel system of a language. Even in a language like Czech where every short vowels has a long counterpart and the length is preserved regardless of stress, things are not always completely straightforward. The puzzling thing is that even though length is fully phonemic in Czech, the loss of the diacritics (such as in the early days of email) leads to only a minimal increase in ambiguity.